There are several known techniques in the prior art use to maintain synchronization between applications in an architecture in which sender and receiver applications use one and the same nominal reference frequency. Most of these known techniques focus on synchronizing the receiver (consumer) application clock with the sender application clock.
In a first prior-art synchronization technique (described in “Understanding Jitter and Wander Measurements and Standards”, Agilent Technologies, 5988-6254EN, 2003, especially FIG. 12.5), the clocks continue to be used independently and there is no automatic control of frequency for the clocks. This first technique relies on the use of a method for the regulation of the throughput rate in the receiver node (called a slip buffer). It consists if the insertion or elimination of a piece of applicative data depending on the divergence in rhythm observed between the throughput rate of data coming from the network and the read rate by the receiver application. One drawback of this first technique is that it does not provide for the integrity of the data except when the precision in the nominal value of the clock frequencies is 0 ppm. If not, it is up to the receiver application to set up means to mask the defects of integrity of the data, A second prior-art synchronization technique (described in the U.S. Pat. No. 6,791,987), called adaptive memory or adaptive buffer consists in setting up an automatic control between the read frequency in the receive node as a function of the level of filling of a memory containing the applicative data coming from the communications network. This second known technique is used to accelerate the reading rate when the quantity of data in the reception memory goes beyond a predetermined threshold or to slow down the reading rate when the quantity of data in the reception memory falls below a predetermined threshold. However, one drawback of this second technique is that it necessitates the addition of developed smoothing methods in order to achieve the integration in time of measurements observed at specific times and thus prevent a jitter effect of the regenerated applicative frequency. Because of the compromise between the maximum time taken for the correction of a drift and the frequency precision with respect to the correction made, this type of method is ill suited to the quality of service requirements imposed on and expected from multipoint synchronous applications.
A third prior-art synchronization technique (described in the U.S. Pat. No. 6,327,273) makes direct use of the network cycle to generate the source and destination applicative clocks. In this case, each source and destination terminal multiplies its network cycle by a same value in order to generate its applicative clock. This third technique necessitates a mode of distribution of the network clock which sets up an automatic control between the network cycles at each terminal. One drawback of this third technique is that it cannot be used to support applicative clocks whose frequencies are independent (i.e. not a multiple or sub-multiple) of the clock frequency of the reference network.
A fourth prior art synchronization technique (described in the patent application EP1052793A1) relies on the periodic dispatch by the source application of temporal information pertaining to time offsets between the events of the source applicative clock and events of the network clock. These pieces of temporal information or synchronous residual time stamps are intended for the computation at the sink node of a drift between source applicative clocks and destination applicative clocks through the network cycle and for setting up an automatic control accordingly between the destination applicative clock frequency and the source applicative frequency, depending on the content of the temporal information received. This fourth prior art technique dictates the setting up in the communications network of a service to ensure constant transfer time of this information, between the instant at which a piece of data is written by the source applicative clock and instant at which this piece of data is made available to the automatic control function of the destination applicative clock in the sink node. With regard to this constraint, this fourth technique can actually be used only in synchronous networks in which the nominal source clock of the application and the network reference clock have a relationship of proportionality between respective nominal values.